A typical semiconductor device formed into ICs has internally a large number of basic functional circuits, such as amplifier circuits, comparator circuits, and/or reference voltage generator circuits, with high integration density. An example of such semiconductor device is a regulator IC comprising an internal circuit with a configuration shown in the circuit diagram of FIG. 2.
Referring to the circuitry of FIG. 2, a main current path of a transistor Q1 of PNP type is connected in series between an input terminal 1 and an output terminal 2, and a base of the transistor Q1, is connected to a ground via a main current path of a transistor Q2 of PNP type. A resistor R13 is arranged between the base and an emitter of the transistor Q1 and resistors R1 and R2 are arranged as connected in series between the output terminal 2 and a ground. There are also configured a power supply circuit 4b, a reference voltage generator circuit 5, and an error amplifier circuit 6, in which the power supply circuit 4b is arranged between the input terminal 1 and a power supply terminal for the reference voltage generator circuit 5 and the error amplifier circuit 6 to connect them together. One of the input terminals of the error amplifier circuit 6 is connected to an output terminal of the reference voltage generator circuit 5, while the other input terminal of the error amplifier circuit 6 is connected to a junction point of the resistor R1 and the resistor R2, and an output terminal of the error amplifier circuit 6 is connected to a base of the transistor Q2.
Herein, the power supply circuit 4b, the reference voltage generator circuit 5 and the error amplifier circuit 6 are respectively configured as described below.
An emitter of a transistor Q41 of PNP type is connected to the input terminal 1, and a collector thereof is connected via a resistor R8 and a diode D43 to a ground. A resistor R8 is arranged between a base of the transistor Q41 and the input terminal 1, a main current path of a transistor Q42 of NPN type is arranged between the base of the transistor Q41 and a ground, and a diode D41 is arranged between the base and the collector of the transistor Q41. A base of the transistor Q42 is connected via a resistor R4 to a control input terminal 3, thus to configure the power supply circuit 4b. 
Further, to the collector of the transistor Q41, which is a component of the power supply circuit 4b, are connected the respective emitters of transistors Q51 and Q52, each being of PNP type. Respective bases of the transistors Q51 and Q52 are connected with each other, and a collector and the base of the transistor Q51 are interconnected. Each collector of the transistors Q51 and Q52 is respectively connected to each collector of NPN type transistor Q53 or Q54. Respective bases of the transistors Q53 and Q54 are connected with each other, and the collector and the base of the transistor Q54 are interconnected. An emitter of the transistor Q53 is connected via a series circuit composed of resistors R10 and R11 to a ground, and an emitter of the transistor Q54 is connected to a junction point of the resistors R10 and R11. A main current path of a transistor Q55 whose base is in connection with a junction point of the resistor R8 and the diode D43 of the power supply circuit 4b is arranged as connected in parallel with a main current path of the transistor Q53, thus to configure the reference voltage generator circuit 5.
Then, each of emitters of PNP type transistors Q61 and Q62 is connected to the collector of the transistor Q41, which is a component of the power supply circuit 4b. Respective bases of the transistors Q61 and Q62 are connected with each other, and a collector and the base of the transistor Q62 are interconnected. Each of collectors of the transistors Q61 and Q62 is respectively connected to each collector of NPN type transistor Q63 or Q64. Respective emitters of the transistors Q63 and Q64 are connected with each other, and a resistor R12 is arranged between a common junction point of the respective emitters and a ground. A base of the transistor Q63 is connected to the collector and the base of the transistor Q54 which is a component of the reference voltage generator circuit 5, and a base of the transistor Q64 is connected to a junction point of the resistors R1 and R2. A junction point of the collectors of the transistors Q61 and Q63 is connected to the base of the transistor Q2, thus to configure the error amplifier circuit 6.
In the circuitry of FIG. 2, which has been configured as described above, an increased level of a control signal applied to the control input terminal 3 turns on the transistors Q42 and Q41. Thereby, a drive voltage from an external power source connected to the input terminal 1 is supplied via the transistor Q41 of the power supply circuit 4b to each of the internal circuitries of the reference voltage generator circuit 5 and the error amplifier circuit 6.
In the reference voltage generator circuit 5 supplied with the drive voltage, upon starting the circuit, at first the transistor Q55 is turned on, and a current mirror circuit composed of the transistors Q51 and Q52 is made operative. Secondarily, another current mirror circuit composed of the transistors Q53 and Q54 is made operative, which has been supplied with the current from the transistors Q51 and Q52, and in turn the transistor Q55 is turned off as the transistor Q53 is turned on. After that, the activated reference voltage generator circuit 5 would generate a reference voltage of about 1.25V, based on a band gap of the semiconductor material, at the positions of collector and the base of the transistor Q54.
On the other hand, in the error amplifier circuit 6, which has been supplied with the drive voltage, at first the transistor Q63 supplied with the reference voltage conducts, and thereby the transistors Q2 and Q1 conduct. As the transistor Q1 has conducted, an electric power from the input terminal 1 is transmitted via the transistor Q1 to the output terminal 2, and thus an output voltage is generated on the output terminal 2. The output voltage generated on the output terminal 2 is divided by the resistors R1 and R2, which in turn is supplied to the base of the transistor Q64. Subsequently, the transistor Q64 conducts to make operative the current mirror circuit composed of the transistors Q61 and Q62. After that, the activated error amplifier circuit 6 would control the current flowing through the transistors Q2 and Q1 in response to the reference voltage supplied to the transistor Q63 and the divided voltage supplied to the transistor Q64 so as to regulate the magnitude of the output voltage to be constant.
In such a circuitry as shown in FIG. 2, the reference voltage generator circuit 5 and the error amplifier circuit 6 are connected via the transistor Q41 in on-state and the input terminal 1 to the external power source. Owing to this configuration, if a voltage supplied from the external power source fluctuates, the reference voltage generator circuit 5 and the error amplifier circuit 6 would be subject to a direct effect of the voltage fluctuation. In addition, there has been a problem that each of the transistors Q51, Q52, Q61 and Q62, each being of PNP type, arranged in the power source side of each of the circuits 5 and 6 tends to suffer from the Early effect seriously when a high voltage is applied, or that the transistors of PNP type are subject to the effects of variations in various conditions in the manufacturing processes, resulting in the characteristic value of each product to be varied widely.
Because of these reasons mentioned above, the circuitry employing the configuration of FIG. 2 is especially subject to the effect of the voltage fluctuation, which has made it difficult to improve and homogenize the ripple rejection characteristics against the fluctuation in the input voltage to the semiconductor device.
For such a circuitry as shown in FIG. 2, an attempt has been made to improve the characteristics by designing the power supply circuit with a configuration as shown in FIG. 3.
Referring to the circuitry of FIG. 3, each of emitters of PNP type transistors Q48 and Q49 is connected to the input terminal 1. Respective bases of the transistors Q48 and Q49 are connected with each other, and a collector and the base of the transistor Q48 are interconnected. A resistor R9 and a main current path of a transistor Q42 are arranged between the collector of the transistor Q48 and a ground to be connected in series, and a base of the transistor Q42 is connected via a resistor R4 to the control input terminal 3. A collector of the transistor Q 49 is connected to a base of a NPN type transistor Q410, and a plurality of diodes D44-D48 is arranged between the collector of the transistor Q49 and a ground to be connected in series. Then, a collector of the transistor Q410 is connected to the reference voltage generator circuit 5 and the error amplifier circuit 6, and a power supply circuit 4c has been thus configured.
In the power supply circuit 4c configured as described above, an increased level of control signal applied to the control input terminal 3 brings the transistor Q42 into on-state so as to activate a current mirror circuit composed of the transistors Q48 and Q49. A part of the current passed through the main current path of the transistor Q49 flows via the serially connected diodes D44-D48 into the ground, while the potential at a point of the base of the transistor Q410 is raised up by a forward voltage generated in the diodes D44-D48. Subsequently, the transistor Q410 operates so that a combined value of a voltage at a point of the emitter thereof and a voltage between the base and the emitter thereof is made equal to a voltage at a point of the base thereof, and thus a drive voltage to be supplied to the reference voltage generator circuit 5 and the error amplifier circuit 6 is made almost equal to a magnitude determined by subtracting the voltage between the base and the emitter of the transistor Q410 from the total of forward drop voltages generated in the diodes D44-D48. Thereby, even if the input voltage would fluctuate, the fluctuation in the drive voltage could be controlled so as to be smaller than that in the input voltage, so that the ripple rejection characteristics of the semiconductor device against the fluctuation in the input voltage could be improved and homogenized.
It should be noted that, when a reference voltage generator circuit of band gap type similar to that shown in FIG. 2 is employed as a reference voltage generator circuit 5 of FIG. 3, a drive voltage to be supplied to the reference voltage generator circuit 5 is required to have a voltage value of approximately equal to or more than 1.8V. In the circuitry with the configuration shown in FIG. 3, this drive voltage is determined by the total of the forward voltage drops of the diodes D44-D48.
A magnitude of the forward voltage drop of a diode element is about 0.7V per one element at ambient temperature of about 20xc2x0 C. To make the drive voltage be 1.8V or more, with a voltage between the base and the emitter of the transistor Q410 taken into account, four pieces of diode elements are needed. However, since a diode element has a temperature characteristic of about xe2x88x922 mV/xc2x0 C., another piece of diode must be added to make the drive voltage not to drop under 1.8V over the range of operating temperature of the semiconductor device. Accordingly, the power supply circuit 4c shown in FIG. 3 should have the total of five or more diode elements connected in series.
In such a case, a voltage to be supplied from the external power source to the semiconductor device is required to have a voltage value equal to or more than 3.5V, which is equivalent to the total of the forward voltage drops of the diodes D44-D48 added with the voltage between the collector and the emitter of the transistor Q49. However, the current market requires a semiconductor device to have a minimum operating voltage value of 2.5V, which has not been achieved by the semiconductor device employing the power supply circuit 4c of FIG. 3 which requires to have a voltage value equal to or more than 3.5V.
Accordingly, an object of the present invention is to improve the ripple rejection characteristics and to reduce the operating voltage of a semiconductor device.
Above object can be accomplished by the present invention which provides a semiconductor device comprising: an input terminal connected to an external power source; an internal circuit including a reference voltage generator circuit; and further a power supply circuit located between said input terminal and said internal circuit so as to make a connection therebetween, said power supply circuit having a first transistor for supplying said internal circuit with a drive voltage and a second transistor for passing a current therethrough in response to a magnitude of a reference voltage outputted from said reference voltage generator circuit and a magnitude of said drive voltage, wherein said drive voltage is lower than the voltage supplied to said input terminal but is higher than the reference voltage outputted from said reference voltage generator circuit.